The present invention relates to a production system and production process of an aromatic polycarbonate. More specifically, the present invention relates to a production process and production system which can produce an aromatic polycarbonate which exhibits excellent hue stability and thermostability at the time of production and is excellent in hue and transparency efficiently.
An aromatic polycarbonate resin has excellent properties including impact resistance and transparency. Therefore, it is widely used as a very useful resin. As a process of producing the aromatic polycarbonate resin, an interface process in which an aromatic dihydroxy compound is reacted with phosgene in a mixed solution of an organic solvent and an alkaline solution and a melt-polycondensation process in which an aromatic dihydroxy compound is reacted with a carbonic diester in the presence of a catalyst at a high temperature and under a reduced pressure and produced phenol is removed from the system can be used.
In the case of the melt-polycondensation process, a reaction mixture remaining molten at a high temperature moves between aromatic polycarbonate processing plants or is discharged from the aromatic polycarbonate processing plants.
While moving between the aromatic polycarbonate processing plants or being discharged from the aromatic polycarbonate processing plants, the molten reaction mixture is exposed to high temperatures, whereby it may become colored or foreign materials may be produced in the mixture. As a result, excellent properties such as transparency of an aromatic polycarbonate are impaired.
In particular, in the case of an aromatic polycarbonate intended for an optical application such as a compact disk, coloration and foreign materials are not preferable from the viewpoint of product quality.
Japanese Patent Laid-Open Publication No. 10-7783 discloses a process using a downstream pipe which has an average gradient of not lower than 1% and satisfies the following expression:
A/(A+B+C+D) greater than 0.9 
wherein A is a length of a downstream pipe having a gradient of not lower than 1%, B is a length of a downstream pipe having a gradient of lower than 1%, C is a length of a horizontal pipe, and D is a length of an upstream pipe, as a pipe for transporting a molten polymer having a number average molecular weight of not smaller than 4,000 when polymerizing an aromatic dihydroxy compound and diaryl carbonate in a molten state by use of at least one polymerizer so as to produce an aromatic polycarbonate and a system for producing an aromatic polycarbonate which is characterized by use of a pipe as described above.
Japanese Patent Laid-Open Publication No. 10-226723 discloses a process for producing an aromatic polycarbonate by a melt-polycondensation process, wherein a transporting speed of a molten polymer is set at 0.05 m/sec or higher when the molten polymer has a number average molecular weight of smaller than 2,500 and at 0.005 m/sec or higher when the molten polymer has a number average molecular weight of not smaller than 2,500.
Japanese Patent Laid-Open Publication No. 10-330473 discloses a process for producing an aromatic polycarbonate by a melt-polycondensation process, wherein a pipe for transporting a molten polymer having a number average molecular weight of not smaller than 4,000 has 50 bends or less.
Japanese Patent Laid-Open Publication No. 2000-119388 discloses a process for producing an aromatic polycarbonate by a continuous melt-polycondensation process, wherein a flow rate of a reaction mixture in a pipe through which the molten reaction mixture passes is not lower than 0.5 cm/sec.
Japanese Patent Laid-Open Publication No. 2001-163968 discloses a process for producing an aromatic polycarbonate by a melt-polycondensation process, wherein a pipe for transporting a molten polymer having a viscosity average molecular weight of 4,000 to 30,000 has up to 40 flanges.
Further, Japanese Patent Laid-Open Publication No. 2001-226478 discloses a process for producing an aromatic polycarbonate having a viscosity average molecular weight of not smaller than 15,000 by a melt-polycondensation process, wherein a pipe for transporting a reaction solution having a viscosity average molecular weight of not smaller than 3,000 is a double-layer pipe comprising an inner pipe and an outer pipe with a heating medium therebetween, the reaction solution is caused to flow through the inner pipe of the pipe such that the following expression (1):
uxe2x89xa7exp{xe2x88x920.21n(xcexc)xe2x88x923.8}xe2x80x83xe2x80x83(1) 
wherein u is a pipe flow rate (m/s) which is a numerical value obtained by dividing a flow rate of the reaction solution by a cross section of the transport pipe, and xcexc is the reaction solution""s viscosity (Paxc2x7S) at an inlet of the transport pipe, is satisfied and average residence time is within 900 seconds, and a temperature of a heating medium in the outer pipe of the pipe is maintained at temperatures ranging from a temperature of the reaction solution in an upstream reactor connected to the pipe to the reaction solution temperature +50xc2x0 C.
However, in all the above melt-polycondensation processes, specific considerations are not given to specific possible problems hindering a polycondensate transported in a pipe from flowing through the pipe.
It is an object of the present invention to provide a process for producing an aromatic polycarbonate which hardly undergoes coloration and production of foreign materials.
It is another object of the present invention to provide a process for producing such an aromatic polycarbonate of excellent quality as described above by controlling a flow of a reaction mixture which flows through a self-lubricating gear pump and a pipe having the gear pump and at least one of a bend, a valve and a detecting probe.
It is still another object of the present invention to provide a producion system suitable for performing the process of the present invention for producing such an aromatic polycarbonate as described above.
Other objects and advantages of the present invention will be apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are achieved by a process for producing an aromatic polycarbonate by melt-polymerizing an aromatic dihydroxy compound and a carbonic acid diester in the presence of a catalyst continuously in multi steps in a plurality of polycondensation vessels connected to each other in series via pipes, wherein at least one of the pipes has a self-lubricating gear pump and reduced numbers of bends and locations of valves and detecting probes so that a total of flow inhibition strengths become 10 or less, and a polycondensate is fed into the at least one of the pipes such that the following expressions (1) and (2):
Q/Sxe2x89xa70.1xe2x80x83xe2x80x83(1) 
wherein Q is a flow rate (cm3/sec) of a polycondensate to be continuously fed into a passage of a shaft seal portion of the self-lubricating gear pump, and S is a cross-sectional area (cm2) of the passage of the shaft seal portion of the self-lubricating gear pump,
Dxe2x89xa62.9xc3x97W1/3xe2x80x83xe2x80x83(2) 
wherein D is an internal diameter (cm) of the pipe, and W is a flow rate (cm3/sec) of the polycondensate, are satisfied simultaneously,
provided that flow inhibition strength corresponding to one bend or one location of the valve is 1 and flow inhibition strength corresponding to one location of the detecting probe is 0.5.
According to the present invention, secondly, the above objects and advantages of the present invention are achieved by a production system for producing an aromatic polycarbonate by melt-polycondensing an aromatic dihydroxy compound and a carbonic acid diester in the presence of a catalyst continuously, the system comprising:
a plurality of polycondensation vessels connected in series to each other,
an extrusion die connected to the lowest downstream polycondensation vessel via a polymer filter, and
pipes between all the polycondensation vessels and between the lowest downstream polycondensation vessel and the extrusion die,
wherein all the pipes except for one between first and second upstream polycondensation vessels have a self-lubricating gear pump and also have valves, bends and detecting probes such that a total of flow inhibition strengths become 10 or less, provided that flow inhibition strength per valve or bend is 1 and flow inhibition strength per detecting probe is 0.5.
Further, according to the present invention, thirdly, the above objects and advantages of the present invention are achieved by a production system for producing an aromatic polycarbonate by melt-polycondensing an aromatic dihydroxy compound and a carbonic acid diester in the presence of a catalyst continuously, the system comprising:
a plurality of polycondensation vessels connected in series to each other,
an extruder connected to the lowest downstream polycondensation vessel,
an extrusion die connected to the extruder via a polymer filter, and
pipes between all the polycondensation vessels, between the lowest downstream polycondensation vessel and the extruder and between the extruder and the extrusion die,
wherein all the pipes except for one between first and second upstream polycondensation vessels have a self-lubricating gear pump and also have valves, bends and detecting probes such that a total of flow inhibition strengths become 10 or less, provided that flow inhibition strength per valve or bend is 1 and flow inhibition strength per detecting probe is 0.5.
Further, according to the present invention, fourthly, the above objects and advantages of the present invention are achieved by a production system for producing an aromatic polycarbonate, the system comprising an extruder, an extrusion die, and a pipe connecting the extruder and the extrusion die with each other via a polymer filter, wherein the pipe has valves, bends and detecting probes such that a total of flow inhibition strengths become 10 or less, provided that flow inhibition strength per valve or bend is 1 and flow inhibition strength per detecting probe is 0.5.